The invention is directed to a suspension device, in particular for a bicycle, with at least one reciprocating cylinder device featuring an axial supported sliding piston in the inner cavity of the cylinder. The cylinder is closed at the opposing ends by end walls, and the piston is connected to a piston rod which pushes against one of the end walls. Both sides of the piston are surrounded by the working space bordering the piston and the end walls, and which is filled with a working gas and is sealed airtight in operation. A filling device is provided for filling the working space with the working gas.
A suspension device of this type is known from WO 99/03721. It features working spaces on both sides of the piston which are separated from each other by the piston, limited by the cylinder and one of the end walls, and filled with a working gas; and it is sealed airtight when in operation. The piston is situated between the two end walls at a distance from both when at rest. The piston can be moved from its resting position by a reset force caused by the axial sliding within the cylinder against the volume of gas encased in the working spaces.
In doing so, the working gas is compressed inside one of the working spaces and decompressed in the other working space, so that the volume of gas found in the different working spaces exerts a pushing or pulling force on the piston, each corresponding to the product of the gas pressure of the gas found in the working space and the piston surface impinged on by this gas pressure. Since the force exerted on both sides of the piston is mutually compensating when the piston is in its resting position, only a comparatively small deflection force needs to be exerted on the piston to move it from its resting position. Thus, compared to a suspension device with only one working space situated on one of the two sides of the piston, this results in a better response from the suspension device, and therefore a more comfortable suspension. Furthermore, a progressive spring characteristic results from the two working spaces found on both sides of the piston, i.e. the increase in the spring characteristic increases with increasing deflection of the piston from its resting position. In this way, an abutting of the piston against one of the end walls, and therefore an undesirably strong deflection of the piston from its resting position is largely avoided.
A filling device is provided for filling both working spaces with working gas and features a feed opening for each space on the outside of the suspension device. These feed openings are connected to the corresponding working space by a feed line. There is a valve installed in each feed line which prevents the escape of the working gas from the working space. The filling of the working space can take place, for example, by means of high air pressure, which is alternately connected to both feed openings of the working spaces. The filling of the suspension device with the working gas through the working spaces on both sides of the piston is relatively complicated in comparison to a suspension device with only one working space. So it is especially difficult for a layperson who is not thoroughly familiar with the operation of the filling device to for the optimal balance for the suspension through appropriate filling of the different working spaces when dealing with such a suspension device installed on a bicycle.
The object exists, therefore, of creating a suspension device of the type mentioned in the introduction which makes it possible to adjust the suspension device simply through a simple method of filling the working spaces with the working gas.
The solution to this problem is found in a suspension device like that mentioned in the introduction which is provided with a filling device featuring a common feed line for filling both working spaces with the working gas, in which a first shut-off device is situated. In this device, the working spaces situated on both sides of the piston are connected to each other by a connecting line in which a second shut-off device is located and which can be operated from outside.
As an advantage, both working spaces can also be filled with the working gas at the same time, which makes a simple management of the suspension device possible. The filling of the working spaces can take place, for example, by first opening the second shut-off device located in the connecting line, and then connecting the feed line to a source of gas pressure or a pump. Next, the first shut-off device located in the feed line is opened, and both working spaces are filled at the same time through the feed line. After or during the filling of the working spaces with working gas, the piston is positioned in the desired position in the cylinder and, with the piston in this position, the second shut-off device is closed, so that both working spaces are then sealed airtight from each other. If needed, the source of gas pressure or the pump can then be separated from the feed line. Of course, the working gas can also be put into only one of the working spaces first by closing the second shut-off device located in the connecting line. After filling this working space with the working gas, the first shut-off device located in the feed line is closed. Then the second shut-off device located in the connecting line is opened so that the working gas can then flow from one working space into the other. As an advantage, the resting position of the piston within the inner cavity of the cylinder can be changed in a simple manner when the second shut-off device located in the connecting line is open, without needing to fill the inner cavity of the cylinder with more working gas or allowing it to escape. The first shut-off device located in the feed line is preferably a valve operated by the pressure of the working gas.
It is advantageous if the connecting line between the working spaces penetrates the piston and if the shut-off device located in the connecting line is connected with an operating device which penetrates an inner cavity of the piston rod and is located on the outer end of the piston rod. This results in an especially compactly constructed suspension device, in which the transfer element is situated so on the inside of the hollow piston rod, so as to save space. Therefore, the operating device is located on the free end of the piston rod facing away from the piston, where it is easily accessible for opening and closing the second shutoff device located in the connecting line.
A yet more compact suspension device can be achieved by constructing it so that the working gas feed line penetrates an inner cavity of the transfer element. On the outer end of the transfer element facing away from the piston, a feed/escape opening for the working gas can then be provided in the vicinity of the operating device, for example, which is connected by the feed line with a feed line opening leading to one of the working spaces located on the other end of the transfer element.
In a prototype of the invention, the inner cavity of the piston rod penetrates the piston and forms the continuation of the feed line by connecting to the inner cavity of the transfer element. The feed line constructed to penetrate the inner cavity of the transfer element can then be connected simply for filling with or discharging of the working gas through the inner cavity of the piston rod penetrating the piston with the working space located on the side of the piston facing away from the operating device of the second shut-off device located in the connecting line.
In a preferred embodiment of the invention, the hollow piston rod, which is connected to one of the working spaces by its inner cavity, features an opening on the side for the working gas leading to the other working space. A slide valve for closing and opening this opening is provided on the inner end of the transfer device. The second shut-off device located in the connecting line and formed by the opening on the side and the slide valve is then located in the inside of the piston rod, thus achieving an especially compact construction.
The slide valve is conveniently constructed as a sealing piston feeding into the piston rod, which can be moved into a closed position covering the opening on the side and into an open position when pulled out. The slide valve then feeds especially well into the inner cavity of the piston rod, which makes possible a good, airtight seal of both the working spaces located on either side of the piston. The slide valve constructed as a piston can, if need be, feature sealing rings opposite each other around its circumference in the axial direction. In the closed position, these sealing rings are located on the slide valve on both sides of the opening.
It is especially advantageous if the cylinder is cup-shaped and constructed with the cylinder housing in one piece with one of the end walls. On the opposite end wall, a seal can be provided which seals the piston rod against this end wall.
In an especially advantageous embodiment of the invention, the suspension device is constructed as a bicycle fork whose fork legs each feature telescope-like telescoping parts nestled within each other and which can be moved in relation to each other in the extension direction of the fork legs. These telescoping parts each define an inner cavity in which the reciprocating cylinder device of the invention is located. The cylinder of the reciprocating cylinder device is connected with one telescoping part and the piston rod with the other telescoping part. The suspension device then makes a comfortable air suspension of the bicycle frame possible with regard to the steering wheel of the bicycle situated between the free ends of the bicycle fork. Thus, this kind of suspension device can be located in particular on the front steering wheel of a bicycle.
The piston rod is conveniently connected with each upper telescoping part of the fork leg of the bicycle fork when in use, and the operating device, if needed, and a feed opening for the feed line is located on the upper end of the fork leg. The operating device and the feed opening for the feed line are then easily accessed on the upper end of the bicycle fork for filling the working spaces with working gas and/or for altering the resting position of the piston, which is situated so that it can be moved within the cylinder. If needed, the first shut-off device, located inside the connecting line and preferably constructed as a valve, can be situated in the vicinity of the feed opening.